JPH11320651A - Manufacture of crosslinked polyethylene tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain both 'flexibility at normal temperatures' and more excellent 'strength at high temperatures'. SOLUTION: Polyethylene-series resin which is polymerized by using a metallocene compound as a polymerization catalyst and has a density of 0.932-0.940 g/cm<3> , a weight-average molecular weight of 40000-90000 and a molecular weight distribution (by chromatography: Mw/Mn) of 2.0 - less than 4.0 is supplied to an extruder. Then, the polyethylene-series resin is silane-modified in the extruder by grafting a silane compound under the presence of a radical formation agent and it is extruded in the shape of a tube and crosslinked so that a gel rate be 65% or above, while it is helped to be made silanol under the presence of a silanol condensation catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked polyethylene pipe.

[0002]

2. Description of the Related Art In recent years, crosslinked polyethylene pipes have been used as hot water pipes for hot water supply systems and heating systems instead of steel pipes. The cross-linked polyethylene pipe has "flexibility at normal temperature" to reduce the burden on the installer, such as improved insertion into the sheath pipe, and "high temperature strength (yield strength, creep properties) Etc.) are required.

However, flexibility at room temperature generally causes a decrease in strength at high temperatures. Therefore, in the conventional manufacturing technology of crosslinked polyethylene pipes, it is necessary to achieve both flexibility at room temperature and strength at high temperatures. Was not easy.

[0004] In order to solve such a problem, Japanese Patent Laid-Open Publication No. 2-253076 has been proposed.
In this proposed method, the physical properties of polyethylene are set to a density of 0.932 to 0.940 g / cm ³ , the “flexibility at normal temperature” is maintained, and the melt index is 0.1 to
With 0.4 g / 10 min, "high temperature strength (yield strength, creep characteristics, etc.)" is improved. Then, as a production method, a silane compound is grafted to form an uncrosslinked granular compound (first stage), and the compound is formed into a tube while preventing crosslinking (second stage). Alternatively, it has been proposed to react with water releasing substances.

[0005]

However, the polyethylene used in the two-stage molding method described in the above publication has a low melt index (0.1 to 0.4 g / 10 min).
Therefore, the back pressure rises more than necessary at the time of extrusion molding, and an excessive load is applied to the extrusion molding motor and the like, so that molding is difficult.
So instead of lowering the melt index,
By using a polyethylene resin having a weight average molecular weight of 40,000 or more and 90,000 or less and a molecular weight distribution (chromatographic method: Mw / Mn) of 2.0 or more and less than 4.0, which is polymerized using a metallocene compound as a polymerization catalyst, “High temperature strength” can be improved. The polyethylene used in the two-stage molding method described in the above publication is considered to be polyethylene polymerized using a Ziegler catalyst (hereinafter, referred to as a Ziegler-catalyzed polyethylene-based resin), and the polyethylene-based resin using a Ziegler catalyst has a molecular weight distribution. The polymer has a low melt viscosity due to the large content of low molecular weight components due to its large width. For this reason, when the graft polyethylene is extruded in the second stage, extrusion molding is possible even if the crosslinking reaction progresses to some extent due to heating in the barrel. However, when a polyethylene-based resin using a metallocene catalyst having a molecular weight of 40,000 or more and 90,000 or less and a molecular weight distribution (chromatographic method: Mw / Mn) of 2.0 or more and less than 4.0 is used, the molecular weight distribution is narrow and the low molecular weight is low. Since the components are reduced and the contribution of the lowering of the viscosity by the low molecular weight components is reduced, the viscosity of the plasticized resin becomes higher than the resin polymerized using the Ziegler catalyst, and in addition,
Grafting and silane denaturation further increase the viscosity, which makes two-stage molding, such as a Ziegler-catalyzed polyethylene resin, very difficult.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for producing a crosslinked polyethylene tube having both "flexibility at normal temperature" and better "strength at high temperature". I do.

[0007]

The invention according to claim 1 of the present application (invention 1) has a density of from 0.932 to 0.940 g / c polymerized using a metallocene compound as a polymerization catalyst.
m ³ , weight average molecular weight of 40,000 to 90,000, molecular weight distribution (chromatographic method: Mw / Mn) 2.0 or more
After supplying the polyethylene resin of less than 0 to the extruder, the polyethylene resin is grafted with a silane compound in the extruder in the presence of a radical generator to modify the silane, and silanolization is promoted in the presence of a silanol condensation catalyst. And a step of cross-linking to a gel fraction of 65% or more.

The invention described in claim 2 of the present application (Invention 2)
The method according to claim 1, wherein the polyethylene resin has an HMI (high melt melt index) of 45 or more and 85 or less.

As the production method of the present invention, the production is performed not by a two-stage molding method but by a one-stage molding method. In other words, instead of forming a non-crosslinked granular compound by grafting a silane compound before forming into a tubular shape (second stage) as in the two-stage molding method (first stage), it is extruded into a tubular shape. In an extruder, the silane compound is grafted with a silane and the silanolization is promoted, and the extruder is produced in a single step by a molding method. Therefore, extrusion molding can be performed without increasing the viscosity of the polyethylene resin in the extruder.

The properties and the like of the above metallocene compound will be described below. Generally, a metallocene compound is
A compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. A tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, and platinum has one or more cyclopentadiene rings. Or a compound whose analog is present as a ligand (ligand).

Examples of the ligand include a cyclopentadienyl ring, an indenyl ring, a cyclopentadienyl ring and an indenyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon monosubstituted metalloid group, and a cyclopentadienyl ring. Enyl oligomer rings and the like.

In addition to these π-electron unsaturated compounds,
For example, monovalent anions or divalent anion chelates such as chlorine and bromine, hydrocarbon groups, alkoxides, amides, phosphides, arylalkoxides, arylamides, aryl phosphides, aryl oxides, etc. are coordinated to transition metals. It may be.

Examples of the hydrocarbon group substituted with the cyclopentadienyl ring and the indenyl ring include, for example, methyl, ethyl, propyl, butyl, isobutyl, amyl,
Isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, nonyl, decyl, cetyl, phenyl and the like.

Examples of such metallocene compounds include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethyl Cyclopentadienyl-tert-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium dichloride, methylphenylsilyl Tetramethylcyclopentadienyl-tert-butylamido hafnium dichloride, indenyl titanium tris (dimethylamide), indenylthi Niumutorisu (diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

These metallocene compounds function as catalysts in the polymerization of olefins such as ethylene by changing the type of metal and the structure of the ligand and combining them with a specific cocatalyst (co-catalyst). Specifically, the polymerization is carried out by reacting a metallocene compound with methylaluminoxane (MA) as a cocatalyst.
O), a boron compound or the like is added. The use ratio of the cocatalyst to the metallocene compound is 10 to 1,0
It is 0.00000 mole times, preferably 50 to 5000 mole times.

The above polymerization conditions are not particularly limited.
For example, a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, a gas phase polymerization method, and the like can be used. Generally, the polymerization temperature is -100 to 300 ° C, and the polymerization pressure is normal pressure to 100 kg / cm 2.

Examples of the polyethylene resin include a homopolymer of ethylene and a copolymer of ethylene and an α-olefin. As an α-olefin,
For example, propylene, 1-butene, 1-pentene, 1-
Hexene, 4-methyl-1-pentene, 1-heptene,
1-octene and the like.

Actually, examples of a polyethylene resin obtained by using a metallocene compound as a polymerization catalyst (hereinafter referred to as “polyethylene resin using a metallocene catalyst”) include, for example, HF manufactured by Dow Chemical Company and Exxon Chemical Company. EXACT and the like are commercially available.

The metallocene catalyst (compound) having such a structure is characterized in that the properties of each active site are uniform. That is, since the activity of each active site is equal, the molecular weight, molecular weight distribution, composition, and uniformity of the composition distribution of the polymer to be synthesized are improved. Therefore, by using a metallocene catalyst during the production of a polyethylene resin, it is possible to obtain a polyethylene resin having a narrower molecular weight distribution than when a conventional Ziegler catalyst is used. Also L-LDP
For E (linear low density polyethylene), butene,
Copolymerization with higher olefins such as hexene and octene is generally performed. By using a metallocene catalyst, the higher olefins are evenly added to the polyethylene chain, thereby obtaining a copolymer having a homogeneous structure. Obtainable.

Therefore, the polyethylene-based resin using a metallocene catalyst is composed of lamellar layers having a uniform thickness, and the amount of molecules (tie molecules) binding each layer of the lamellar layers to the conventional Ziegler catalyst It is increased compared to the polyethylene resin used, whereby a resin having better breaking properties can be obtained.

[0021] The silane compound used in the present invention is a silane compound having an olefinic unsaturated bond and a hydrolyzable organic group. With such features, preferred silane compounds for use in the present invention include:
For example, there is vinyltrisalkoxylan,
Vinyl trimethoxy silane, vinyl triethoxy silane, and vinyl tris (methoxy ethoxy) silane are preferred. Further, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane and the like may be used.

The olefinic unsaturated bond site of the silane compound reacts with a free radical site generated in the polyethylene resin. Examples of the radical generator that generates the radical and that is preferable in the present invention include organic peroxides and organic peresters, among which benzoyl peroxide, dichlorobenzoyl peroxide,
Dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (peroxybenzoate) hexyne-3, 1,4-bis (tert-butylperoxyisopropyl) benzene, lauroyl peroxide, tert-butyl Peracetate, 2,5
-Dimethyl-2,5-di (tert-butylperoxy) hexyne-3,2,5-dimethyl-2,5-di (t
tert-butylperoxy) hexane, tert-butylperbenzoate, tert-butylperphenylacetate, tert-butylperisobutyrate, te
rt-butyl per-sec-octoate, tert-
Butyl perpivalate, cumyl perpivalate, ter
T-butyl perdiethyl acetate and the like are preferable. In addition, there are azo compounds such as azobis-isobutylnitrile and dimethylazoisobutyrate.

It is preferable to use a radical generator having a one-minute half-life temperature of 165 ° C. or more and 190 ° C. or less. When the one-minute half-life temperature is lower than 165 ° C., the amount of radical generation increases remarkably in the initial stage of the reaction, so that the control of the reaction becomes difficult and it becomes difficult to set stable molding conditions. From the cross-linking reaction, a gelled product having a transparent spherical appearance, generally called scorch, is generated in the product, which easily causes problems such as deterioration of the appearance of the product and reduction in strength. On the other hand, when the temperature exceeds 190 ° C., the amount of grafting of the silane compound is reduced when the plasticized resin undergoes silane modification, so that the gel fraction is 65%.
Otherwise, the creep characteristics of the molded product are inferior.

The silanol condensation catalyst used in the present invention may be any compound generally used as a catalyst for promoting dehydration condensation between silanols. Examples thereof include dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctoate. Compounds such as stannous acetate, cobalt naphthenate, lead naphthenate, ethylamine, dibutylamine, hexylamine, pyridine, inorganic salts such as sulfuric acid and hydrochloric acid, toluenesulfonic acid, acetic acid, stearic acid, and maleic acid. One or more of these are preferably used, and among them, dibutyltin dilaurate is more preferably used.

Generally, when a conventional Ziegler-catalyzed polyethylene-based resin is subjected to a crosslinking treatment, creep characteristics, yield strength, and the like are improved due to the presence of the crosslinking molecule. However, on the other hand, since the crystal structure is disturbed by the cross-linking molecules, fragile parts are generated in the solid structure, stress concentration occurs,
A remarkable improvement in strength cannot be expected.

On the other hand, in the polyethylene resin using a metallocene catalyst, as described above, since the respective polymerization components are uniformly distributed in the polymer, disorder of the crystal structure due to crosslinking can be minimized. Therefore, more excellent strength can be obtained.

These will be described with reference to Table 1. In this table, crystal melting data measured using a differential scanning calorimeter (DSC) (before crosslinking of a polyethylene resin using a metallocene catalyst, a polyethylene resin using a Ziegler catalyst,
Each data after crosslinking) is shown.

[0028]

[Table 1]

Here, the DSCpeak half width refers to the temperature width at half the height of the crystal melting peak. Comparing the half widths in this table, before crosslinking, the polyethylene resin using the metallocene catalyst was 0.9 (° C) higher than the polyethylene resin using the Ziegler catalyst.
Narrow, after crosslinking, the latter is 4.8 (°
C) It is narrow.

This means that the polyethylene resin using the metallocene catalyst has a more uniform component distribution and the thickness of the lamella layer is more uniform compared to the polyethylene resin using the Ziegler catalyst. This indicates that the latter crosslinked product is more uniformly distributed with respect to the crosslinked product. It also shows that the lamellar layer having a uniform thickness has a more remarkable effect through the cross-linking treatment.

For these reasons, the metallocene-catalyzed polyethylene-based resin exhibits uniform crosslinking upon addition of the silane compound. Therefore, by sufficiently dispersing and distributing the crosslinking agent, a crosslinked polyethylene tube having a uniform crystal distribution can be obtained. (For this crystal distribution, X
Proof can be made by analytical means such as small-angle line scattering.)

Therefore, it is possible to avoid concentration of stress on the fragile portion when applying stress, and to provide high-temperature strength (yield strength, creep characteristics) superior to that of a conventional crosslinked polyethylene pipe having a non-uniform crystal distribution. be able to.

As the polyethylene resin using a metallocene catalyst used in the present invention, the molecular weight distribution of the starting polyethylene resin (chromatographic method: Mw / Mn, where Mw is the weight average molecular weight, Mn is the number average molecular weight) 2.0
More than 4.0. If the molecular weight distribution is less than 2.0, the viscosity of the plasticized resin becomes high, so that molding is difficult, and if it is more than 4.0, the creep characteristics of the molded article deteriorate.

When the molecular weight distribution is within the above range, the low molecular weight components are reduced and the molecular weights are relatively uniform, so that the contribution of the lowering of the viscosity by the low molecular weight components is reduced. Therefore, the polymerization was carried out using a Ziegler catalyst. The viscosity of the plasticized resin becomes higher than that of the resin. In addition, by grafting and denaturing with silane, the viscosity further increases, so that two-stage molding such as a Ziegler-catalyzed polyethylene resin becomes very difficult.

The polyethylene resin using a metallocene catalyst used in the present invention has a very good crosslinking efficiency due to a small amount of low molecular weight components, and a gel component is formed at once by forming a certain number of crosslinking points. The molding method cannot be adopted.

As the polyethylene resin using a metallocene catalyst used in the present invention, the weight average molecular weight of the starting polyethylene resin is from 40,000 to 90,000. When the molecular weight is less than 40,000, the crosslinking efficiency becomes poor, and the viscosity becomes high, so that molding becomes difficult. When the molecular weight is 90,000 or more,
The back pressure at the time of extrusion molding rises, and an excessive load is applied to a drive motor or the like during the extrusion period, making molding difficult.

The polyethylene resin using a metallocene catalyst used in the present invention has a HMI (High Weight Melt Index) of 45 as a raw material polyethylene resin.
It is 85 or less. In addition, MI which is usually measured
(Melt index) has a problem that the extrusion load is high in a high shearing state even if the MI is high, and it is not possible to express an accurate viscosity. Therefore, in the present invention, the HMI
The viscosity was represented by (high melt index).
MI is the amount of extrusion for 10 minutes when a load of 2.15 kg is applied, while HMI is the amount of extrusion for 10 minutes when a load of 21.5 kg is applied. If the HMI is less than 45, the back pressure at the time of extrusion molding increases, and an excessive load is applied to a drive motor or the like during the extrusion period, making molding difficult. HM
When I is 85 or more, the melt viscosity is insufficient and it is difficult to form a tube.

In the present invention, the silane-modified polyethylene tube is crosslinked so as to have a gel fraction of 65% or more, and preferably 70% or more. If the gel fraction does not reach 65%, the creep characteristics of the molded product will be inferior even if polyethylene having a suitable density and viscosity average molecular weight is used.

Hereinafter, a method for measuring the gel fraction will be described.
A sample of crosslinked polyethylene is extracted with a Soxhlet extractor using xylene as a solvent at the boiling point for 10 hours, and the weight of the unextracted residue is measured according to the following equation.

[0040]

(Equation 1)

In the method for producing a crosslinked polyethylene pipe of the present invention, it is preferable to set the resin temperature of the extruder so as not to exceed 35 ° C. from the one-minute half-life temperature of the radical generator. When the temperature of the resin in the barrel exceeds 35 ° C. from the one-minute half-life temperature of the radical generator, the crosslinking reaction of the resin proceeds in the extruder, and a gelled product having a transparent spherical shape, which is generally called scorch, appears in the product. This is likely to cause problems such as deterioration in appearance and strength of the product.

[0042]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an extruder used in the method for producing a crosslinked polyethylene pipe of the present invention.

As shown in FIG. 1, the extruder 1 includes a hopper 11 for supplying a polyethylene resin, a first vacuum bend hole 12 for removing water from the plasticized resin, and a A first inlet 13 for injecting a silane compound and a radical generator, and a second vacuum bend hole 14 for removing unreacted silane compound from the silane-modified resin
A second injection port 15 for injecting a silanol condensation catalyst into the silane-modified resin, and a mold 16 for extruding the resin into a tubular shape.

The present invention has a step of supplying a polyethylene resin using a metallocene catalyst from the hopper 11 to the extruder 1 and grafting a silane compound to the plasticized resin in the presence of a radical generator to modify the silane. .

In the present invention, it is preferable to include a step of removing water from the plasticized resin in the extruder 1 prior to the silane conversion. If water is present, the unreacted silane compound undergoes homocondensation in the extruder 1, and a transparent spherical gelled product generally called scorch appears on the molded product, which deteriorates the appearance and decreases the strength of the molded product. Problem easily occurs. Therefore, a first vacuum bend hole 12 is provided in a portion of the extruder 1 up to a hopper 11 for supplying a polyethylene resin and a first inlet 13 for supplying a silane compound and a radical generator to remove water. Is preferred. It is preferable that the hopper 11 for supplying the polyethylene resin is also provided with a drain hole to remove water.
Also, from the supplied silane compound and radical generator,
It is preferable to remove water as much as possible by using a molecular sheep or the like, because the molding is further improved.

In the present invention, the silanol-condensed catalyst is injected into the silane-modified resin in the extruder 1 from the second inlet 15 and the silane-modified resin is silanolized in the presence of the silanol condensation catalyst. Has a step of promoting it.

In the present invention, it is preferable to include a step of removing the unreacted silane compound from the plasticized resin through the second vacuum bend hole 14 before extrusion molding. When this step is present, it is possible to suppress the formation of a single condensate of the vinylsilane compound and obtain a molded article having good appearance and excellent quality characteristics.

In the present invention, there is a step of extruding into a tube from the mold 16. The present invention includes a step of exposing the extruded tube to a water atmosphere to crosslink to a gel fraction of 65% or more.

[0049]

EXAMPLES The method for producing a crosslinked polyethylene pipe of the present invention will be described below with reference to examples. Example 1 A crosslinked polyethylene pipe was manufactured using the extruder 1 shown in FIG. Polyethylene resin obtained by using a metallocene catalyst as a polymerization catalyst [manufactured by Dow Chemical Company, trade name "HF1030", weight average molecular weight 53600, density 0.935 g / cm3, molecular weight distribution (chromatographic method: Mw / Mn) 2.5, HMI 70g / 10mi
n] 100 parts by weight are supplied from the hopper 11 to the extruder 1 and plasticized, and the first plasticized resin is
The moisture was removed from the vacuum bend hole 12 of.

In the plasticized resin in the extruder 1, 3 parts by weight of vinylethoxysilane and dicumyl peroxide (173 ° C. for a half-life of 1 minute) were supplied from the first injection hole 13 to 100 parts by weight of the resin. The mixture with 0.12 parts by weight was injected, and a silane compound was grafted in an extruder set at a resin temperature of 185 ° C. in the presence of a radical generator to modify the silane. Next, from the silane-modified resin,
Residual monomer was removed from the second vacuum bend hole 14.

Thereafter, 0.0135 parts by weight of dibutyltin dilaurate is injected into the silane-modified resin in the extruder 1 from the second injection hole 15 with respect to 100 parts by weight of the resin to promote silanolation. I let it. Next, after being extruded into a tube from a mold, it was exposed to a water atmosphere and the gel fraction was 65%.
Crosslinking was performed to obtain a crosslinked polyethylene tube.

Example 2 As a polyethylene resin, a polyethylene resin obtained by using a metallocene catalyst as a polymerization catalyst [prototype manufactured by Asahi Kasei Corporation, density: 0.938 g / cm 3, molecular weight distribution (chromatographic method: Mw / Mn) 3.49, weight average molecular weight 72,000, molecular weight distribution (chromatographic method:
Mw / Mn) 3.49, HMI 60 g / 10 min], and a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

Comparative Example 1 As a polyethylene resin, a polyethylene resin obtained by using a metallocene catalyst as a polymerization catalyst [prototype manufactured by Dow Chemical Company, weight average molecular weight 85,000, density 0.
940 g / cm3, molecular weight distribution (chromatographic method: Mw / Mn) 2.8, HMI 30 g / 10 min]
A crosslinked polyethylene pipe was obtained in the same manner as in Example except that was used. Comparative Example 2 As a polyethylene resin, a polyethylene resin obtained by using a metallocene catalyst as a polymerization catalyst [prototype manufactured by Asahi Kasei Corporation, density: 0.934 g / cm3, molecular weight distribution (chromatographic method: Mw / Mn) 3.65. , Weight average molecular weight 78,000, molecular weight distribution (chromatographic method:
Mw / Mn) 3.65, HMI 42 g / 10 min] was used in the same manner as in Example 1 to obtain a crosslinked polyethylene tube.

Comparative Example 3 As a polyethylene resin, a polyethylene resin obtained by using a Ziegler catalyst as a polymerization catalyst [prototype made by Dow Chemical Company, weight average molecular weight 85,000, density 0.9
40 g / cm3, molecular weight distribution (chromatographic method:
(Mw / Mn) 2.8, HMI 75 g / 10 min], and a crosslinked polyethylene pipe was obtained in the same manner as in the example. Comparative Example 4 As a polyethylene resin, a polyethylene resin obtained by using a metallocene catalyst as a polymerization catalyst [prototype manufactured by Dow Chemical Co., Ltd., weight average molecular weight 60000, density 0.
942 g / cm 3, molecular weight distribution (chromatographic method: Mw / Mn) 2.8, HMI 65 g / 10 min]
A crosslinked polyethylene pipe was obtained in the same manner as in Example except that was used.

With respect to the crosslinked polyethylene pipes obtained in Examples 1 and 2 and Comparative Examples 1 to 4, the following items were specified according to the respective methods. Table 1 shows the results. (1) Tensile elastic modulus measurement (flexibility of pipe) This was performed according to JIS-K-7113. (2) Specification of 95 ° C hot internal pressure creep (strength of tube) A circumferential stress of 4.8 MPa is applied to the tube in hot water of 95 ° C, and it is confirmed whether cracking or leakage occurs in one hour. And performed according to JIS-K-6769. Those that did not crack or leak during one hour were indicated by ○, and those that did occur were indicated by x.

[0056]

[Table 2]

As is clear from Table 2, Examples 1 and 2 were used.
In the case of, it can be seen that the tensile modulus and internal pressure creep are well balanced. However, those of the comparative examples are weak in strength and cannot withstand high water pressure at high temperatures.

[0058]

The method for producing a crosslinked polyethylene pipe of the present invention is as described above, so that a crosslinked polyethylene pipe having both "flexibility at normal temperature" and more excellent "strength at high temperature" is used. Obtainable.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an extruder used in the method for producing a crosslinked polyethylene pipe of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 11 Hopper 12 First vacuum bend hole 13 First inlet 14 Second vacuum bend hole 15 Second inlet 16 Mold

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 230: 08) B29K 23:00 105: 24

Claims (2)

[Claims] 1. A polymer obtained by using a metallocene compound as a polymerization catalyst and having a density of 0.932 to 0.940 g / cm ³ ,
After a polyethylene resin having a weight average molecular weight of 40,000 or more and 90,000 or less and a molecular weight distribution (chromatographic method: Mw / Mn) of 2.0 or more and less than 4.0 is supplied to the extruder, the polyethylene resin is converted into a radical in the extruder. A step of extruding into a tube while grafting a silane compound in the presence of a generator to modify the silane and promoting silanolization in the presence of a silanol condensation catalyst, and a gel fraction of 65%
And a method for producing a crosslinked polyethylene pipe. 2. An HMI as the polyethylene resin.
The method for producing a crosslinked polyethylene pipe according to claim 1, wherein (high weight melt index) is 45 or more and 85 or less.